I prefer this dual 1/4cc and 1/2cc O ring gun from Biogenics. http://www.biogenicsltd.com/guns.html I have used the gun for the last 4 years, and love the ability to manipulate the tip of the gun if need be. Sometimes you will run into a cervix that needs to be manipulated a bit in order to properly deposit the semen, I have been happy with the use of the gun. My one suggestion no matter what gun you end up going with, take the skinny plunger part of your gun and put a slight bend in it. This helps prevent the plunger from simply falling out if you tip the gun upside down.
RLAwhitetails, have you had pretty good luck with the sheaths on that gun? I tried using the twist style sheaths before but mine would always split on me.